docs: def get_workflow_graph(promise):
      """Get a graph of a promise."""
      workflow = get_workflow(promise)
  
      dot = Digraph()
      for i, n in workflow.nodes.items():
          dot.node(str(i), label="{0} \n {1}".format(
              n.foo.__name__,
              _format_arg_list(n.bound_args.args)))
  
      for i in workflow.links:
          for j in workflow.links[i]:
              dot.edge(str(i), str(j[0]), label=str(j[1].name))
  
      return dot